Pikas Hit the Trail

They Contain Multitudes

Based on my past newsletter about pikas, these high elevation (generally) balls of cuteness are clearly popular, so I thought I would return to them.

Turns out pikas are quite the travelers. In the beginning, their first big adventure was leaving their home territory of Asia, which they did around 10 million years ago. Those pika most likely walked, not in one momentous trek but over hundreds of generations, out of Asia across a Bering land bridge to North America and eventually spread across the lower 48 states from Oregon to Nebraska. About 5 million years later, another wave of what was most likely another species of pika swept into North America on their own road trip. Paleoecologists had long proposed that the earlier group arrived and spread and had died out before the second cohort showed up but that idea has recently been altered.

“We now infer that there was some interaction between the two groups,” says Kurt Galbreath, a biologist at Northern Michigan University. The evidence does not come from fossils but from parasites. Not only have pikas journeyed far, they also traveled with a retinue, specifically a distinct group of helminths (roundworms, or nematodes, tapeworms, and flukes). Like hangers-on attached to celebrities, these particular parasites focus their attentions, in this case, limiting their adult form to living in pikas. Using genetic analysis of the parasites, which showed that the parasites descended from the older pika colonists also in the living descendants of the younger pika (our local pika harbor these ancient parasites), Kurt and his team determined that the first and second wave pikas had interacted and shared parasites before the second wave apparently outcompeted the first. These more successful pika then evolved into the modern species (Ochotona princeps) found in the western mountains of the lower 48 states. “We had not known this until we saw it in the parasite data,” Kurt says. (Another pika species, O. collaris, inhabits Alaska.)

Two pika parasites studied by Kurt Galbreath. Graphidiella are 1 - 1.5 inches long. Schizorchis are .5 to 2.5 inches long.

He has also studied the more recent history of pikas, in particular, what they did during the last Ice Age, or glacial maximum (LGM). During this extended period of cold, alpine glaciers expanded in the western mountain ranges, including the Cascades. For example, the Nisqually and Cowlitz glaciers on Mt. Rainier extended 19 and 38 miles down their valleys, respectively, compared to their modern extent. During this time of range expansion and general chill in the air some pika offspring sought out new territories, which is typical when life brings you changes. Those that moved lower were successful and those that stayed high were not; the result was that pika ended up surviving at lower elevation. Again, this didn’t happen overnight but was a process of successive and successful generations of pikas moving down short distances.

Fossil evidence shows pika eventually relocated to suitable low elevation habitat from Colorado to Oregon. No fossils flesh out the story in Washington but Kurt told me that genetic evidence indicates that pikas moved east, west, and south of the Cascades, basically away from where ice dominated, and then returned back to the Cascades, subsequent to glacial retreat. I think of this long term migration as a tide of the little lagomorphs ebbing and flooding over thousands of years and thousands of feet of elevation change. The pikas we see in the Cascades may not be great travelers but at least that potential, and perhaps those past experiences, still persist deep in their DNA.

Twice as cute when twice as many.

Unfortunately, those previous, climate-change induced movements were commensurate with a much slower rate of climate change at present. “The fear,” says Kurt, is that “the pikas will essentially be outpaced by warming conditions.” Plus, in contrast to moving down and finding more territory for survival, moving up leads to less suitable terrain as you run out of mountain.

Over the years, as Kurt became a specialist focusing on the parasite story of pikas, he began to more fully appreciate helminths. Often overlooked, parasites provide an ideal “window into the history” of the host, allowing researchers to reconstruct evolutionary and biogeographical stories that fossils cannot. “Whenever I see pikas, I think of them as an ecosystem unto themselves with their parasites, and just as we value biodiversity in other ecosystems, so should we value the rich diversity of hosts and parasites,” says Kurt. As they say, we, whether pika or person, contain multitudes, and the stories our fellow travelers carry, too.